1. Field of Invention
The present invention relates generally to the field of network bandwidth utilization, and specifically in one aspect to conserving available bandwidth on the network to support video services (such as high definition or HD video) over a content-based network such as a cable television network.
2. Description of Related Technology
One significant competitive challenge presently faced by network operators relates to managing and conserving bandwidth. This includes the reclamation of otherwise under-utilized or unused bandwidth such that the service and/or customer base can be expanded without significant modifications or build-outs of the underlying network infrastructure. For example, it is clearly desirable to expand the types and availability of “next-generation” network services, including high-definition (HD) broadcast, VOD, high-speed data, VoIP, Interactive TV, etc. over time, without the need for major capital expenditures or system modifications. Hence, network operators are increasingly focused on techniques for “squeezing” as much capacity out of their existing networks as possible.
Driving the foregoing expansion of services are several other related factors, such as the increased adoption of HD televisions by consumers (especially as their price continues to decline), and the increased prevalence of HD content provided by non-cable service providers. Such service providers may comprise, e.g., satellite direct broadcast (DBS) networks, stand-alone HD services such as VOOMsm , so-called “over-the-air” HD broadcast systems, and even high-speed Internet Protocol (IP) or similar networks (whether via DSL, cable modem, or otherwise), often referred to as “IPTV”. These factors place added emphasis on the cable operator's efficient use their existing infrastructure and its finite bandwidth.
In most cable networks, programs are transmitted using MPEG (e.g., MPEG-2) audio/video compression. Since cable signals are transmitted using Quadrature Amplitude Modulation (QAM) scheme, available payload bitrate for typical modulation rates (QAM-256) used on HFC systems is roughly 38 Mbps. In many deployments, a typical rate of 3.75 Mbps is used to send one video program at resolution and quality equivalent to NTSC broadcast signals. In digital television terminology, this is called Standard Definition (SD) television resolution or service. Therefore, use of MPEG-2 and QAM modulation enables carriage of 10 SD sessions on one RF channel (10×3.75=37.5 Mbps<38 Mbps).
Entertainment-quality transmission of HD signals requires about four times as much bandwidth as SD. For an exemplary MPEG-2 Main Profile—High Level (MP@HL) video compression, each HD program requires approximately 15 Mbps bitrate. Although revenues from HD services and programming may not be four times the revenue from SD service, the ability to offer HD is often critical to cable operators' strategy to be a leader in digital television service offerings.
In the context of a cable network, present day infrastructure provides capacity up to approximately 750 Mhz (with a lesser number of networks being built out to approximately 870 Mhz). As noted above, the bandwidth requirements associated with the aforementioned HD and other next-generation services (even when implementing complementary next-generation video and audio compression algorithms) are very high compared to existing content payloads and services such as standard definition (SD) television.
However, in the short term, even the most optimistic projections for the demand of HD and other such next-generation services would not require all (or even the majority) of the total available capacity of a given infrastructure. Stated differently, many “low-bandwidth”, standard definition (SD) users and providers will exist for years to come. For example, most HD content presently offered is restricted to “prime time” programming, as well as certain sporting events, movies, and other specialized programming; this leaves a large pool of non-HD programming which must also be efficiently supported. Hence, one present goal for the MSO is to manage such heterogeneous (i.e., SD and HD) environments as efficiently as possible.
In U. S. cable systems, downstream RF channels used for transmission each occupy a 6 MHz spectral slot in the available bandwidth (i.e., between approximately 54 MHz and 870 MHz). As previously noted, deployments of the next-generation services (e.g., VOD, HD broadcast/simulcast, PVR/DVR) have to share this spectrum with already established analog and digital cable television services including SD broadcasts. For this reason, the exact RF channel used for a given service may differ from plant to plant. However, within a given cable plant, all homes that are electrically connected to the same cable feed running through a neighborhood will receive the same downstream signal. For the purpose of managing services, these homes are grouped into logical aggregations or clusters typically called Service Groups. Homes belonging to the same Service Group receive their services (e.g., broadcast or VOD service) on the same set of RF channels.
Broadcast programs within the cable network may be unicast (i.e., transmitted within a multiplex on one carrier or QAM and an associated program channel), or multicast (i.e., transmitted over two or more QAMs, each associated with a different program channel). During certain periods, an SD version of a program will be broadcast on one channel, and the HD counterpart thereof broadcast a second channel (SD/HD simulcast). During other periods, the SD version of a program will be broadcast on both channels (SD/SD simulcast).
On-demand service such as VOD is typically offered over a given number (e.g., 4) of RF channels from the available spectrum. Thus, an OD Service Group consists of homes receiving OD signals over the same 4 RF channels. Reasons for this grouping include (i) that it lends itself to a desirable “symmetry of two” design of products (e.g. Scientific Atlanta's MQAM), and (ii) a simple mapping from incoming Asynchronous Serial Interface (ASI) payload rate of 213 Mbps to four QAM payload rates.
From the discussion above, the need for allocation of the bandwidth within the network is evident. One such prior art function, called a Service Resource Manager (SRM), is used for allocating bandwidth based on OD session requests. When a new session (e.g., VOD) request is made, the SRM receives that request, allocates bandwidth on a downstream QAM channel, and sends the information back to the CPE that made the request so that it can tune to the right RF channel and the program therein. Since the SRM controls mapping of incoming session requests to QAM channels within the Service Group, it is an appropriate place for a Cable Operator to enforce RF channel usage policy. In general, the SRM should maximize availability of bandwidth to OD and other sessions (by efficiently recycling bandwidth from expired sessions) and by ensuring some level of redundancy in case of equipment failure (e.g. a QAM modulator goes down). The SRM function can be implemented at the edge or core of the network, in a VOD server, or elsewhere. Depending on where this function is implemented, it is variously referred to as NSG (Network Services Gateway) and SRM (Service Resource Manager).
For example, in a Scientific Atlanta network, the VOD server acts as the service resource manager and asks the Digital Network Control System (DNCS) for specific resources. The DNCS responds with a negative or positive response to the request and the VOD server implements the appropriate logic based on the response.
The SeaChange MediaCluster Server device manufactured by SeaChange International Corporation comprises a group of fault-resilient VOD servers connected over a network, in effect acting as one server. See, e.g., U.S. Pat. No. 5,862,312 to Mann, et al. issued Jan. 19, 1999 and entitled “Loosely coupled mass storage computer cluster” and its progeny. The SeaChange apparatus further includes a session resource manager (SRM), and associated connection manager (CM) and streaming service (SS). The CM ostensibly allocates bandwidth, selecting the best network delivery path over which to stream data to the requesting entity. The SS “optimizes” bandwidth and provides some level of fail-over behavior, such that software component failure will not necessarily cause loss or tear-down of the underlying sessions. No functionality relating to the selective conservation of bandwidth based on different service levels (e.g., SD or HD) is provided within this apparatus, however.
While useful for OD session allocation, the SRM function present in modern cable networks does not provide an adequate mechanism to selectively allocate bandwidth (or more importantly conserve bandwidth) for broadcasts based on their service level, e.g., SD or HD. Furthermore, no adequate mechanism for eliminating the redundancy within the aforementioned SD/SD simulcast paradigm is provided by the SRM, or for that matter any other prior art solution.
Various other schemes for resource and bandwidth management within a cable network are known. For example, U.S. Pat. No. 4,521,881 to Stapleford, et al. issued Jun. 4, 1985 and entitled “Data communication system with increased effective bandwidth” discloses a broadband data communication system that provides increased bandwidth for the transmission of electrical information signals over a coaxial cable having main receive and transmit branches, and having drop line pairs connected to the main branches at junction points. A plurality of user devices are connected to each drop line pair, including a particular set connected to a particular pair. Each user device of the set can transmit and receive signals of local frequencies in a selected bandwidth. Frequency isolation means is connected to the particular drop line pair adjacent its junction point, and passes signals of the local frequencies only from the transmit drop line to the receive drop line, while blocking signals of the local frequencies from transmission over the main cable branches. The particular set of user devices and the filter isolation means together define a subnet. Other subnets can use the same bandwidth of local frequencies without interference, thereby increasing the effective bandwidth of the system.
U.S. Pat. No. 5,963,844 to Dail issued Oct. 5, 1999 entitled “Hybrid fiber-coax system having at least one digital fiber node and increased upstream bandwidth” discloses a method and apparatus for increasing upstream bandwidth and reducing ingress noise in a shared hybrid fiber-coax transmission system. The method comprises modulating at least a portion of upstream signals received from subscribers to a high frequency band (e.g., 750-1000 MHz), thereby increasing the upstream bandwidth. The high frequency upstream signals are then digitally regenerated in the coaxial cable plant prior to receipt at a fiber node. At the fiber node, the high-frequency upstream signals are again digitally regenerated and are then transmitted optically in a baseband digital format between the fiber node and a head end. The digital regeneration of the high frequency upstream signals, and the optical transmission of such signals in a baseband digital format reduces the incidence of ingress noise.
U.S. Pat. No. 6,124,878 to Adams, et al. issued Sep. 26, 2000 entitled “Optimum bandwidth utilization in a shared cable system data channel” discloses a full service network (FSN) providing three communication channels that end between a headend and each set-top within the FSN. These channels comprise (1) forward-application-transport (FAT) channels that supply data from the headend to all or to only addressed ones of the set-tops, (2) a forward-data-channel (FDC) that supplies data from the headend to all or to only addressed set-tops, and (3) a reverse-data-channel (RDC) that supplies data from the set-tops to the headend. A fixed bandwidth FDC provides a first bandwidth portion for the high priority transmission of certain types of items at a continuous bit rate (CBR). All other items are transmitted over the FDC using at an available bit rate (ABR). A priority system for the selective transmission of these other items is based upon (1) how full a data buffer for an item is, as compared to a fullness reference, (2) how old the oldest data in the data buffer for the item is, as compared to an age reference. The fullness reference and the age reference are usually different for each of these other data items.
U.S. Pat. No. 6,169,728 to Perreault, et al. issued Jan. 2, 2001 and entitled “Apparatus and method for spectrum management in a multipoint communication system” discloses an apparatus and method for spectrum management in a cable system that controls upstream channel usage for secondary stations transmitting information to a primary station and downstream channel usage for secondary stations receiving information from a primary station. The apparatus and method controls channel load balancing, channel congestion, and channel assignment in the cable system, and controls upstream channels independently from downstream channels. Factors and parameters utilized in such channel control and allocation include error parameters, channel noise parameters, transmit and receive loading factors, and congestion parameters.
U.S. Pat. No. 6,201,901 to Imajima, et al. issued Apr. 3, 2001 and entitled “Video data distributing device by video on demand” discloses a mechanism that determines whether or not the broadcast of a requested video is to be provided in a FVOD or a NVOD service, and if there is any available channel (bandwidth) for the broadcast. If the broadcast has not been switched from the FVOD service to the NVOD service, then a busy state monitoring mechanism checks the number of the current simultaneous subscribers for the video. If the number is equal to or larger than a threshold, then the busy state monitoring mechanism instructs an NVOD service providing mechanism to broadcast the requested video in the NVOD service. If the number is smaller than the threshold, then the busy state monitoring mechanism instructs an FVOD service providing mechanism to broadcast the requested video in the FVOD service.
United States Patent Publication No. 20020095684 to St. John, et al. published Jul. 18, 2002 end entitled “Methods, systems and computer program products for bandwidth allocation based on throughput guarantees” discloses methods, systems and computer programs for controlling access to a shared communication medium such as a cable network utilizing a revolving priority queue. The revolving priority queue (RPQ) is divided into at least a low priority tier having a plurality of request queues and a high priority tier having a plurality of request queues. A request is directed into an initial queue in the high priority tier if throughput for an end user associated with the request fails to meet a guaranteed throughput. Furthermore, bandwidth may be allocated based on an order in which requests are read from the RPQ, where requests are read from the high priority tier before requests are read from the low priority tier of queues. Additional system embodiments are provided which may be used for requests or for packet-based bandwidth allocation.
United States Patent Publication No. 20020154655 to Gummalla, et al. published Oct. 24, 2002 entitled “System and method for combining requests for data bandwidth by a data provider for transmission of data over an asynchronous communication medium” discloses a method and system for combing requests for data bandwidth by a data provider for transmission of data over an asynchronous communication. A headend receives one or more bandwidths requests from one or more cable modems via upstream communication. A scheduler then combines one or more bandwidths requests from the same cable modem to create a single data burst bandwidth. The headend then grants the data burst bandwidth to the appropriate cable modem via downstream communication.
United States Patent Publication No. 20030140351 to Hoarty, et al. published Jul. 24, 2003 entitled “Cable television system compatible bandwidth upgrade using embedded digital channels” discloses apparatus, methods, and systems for providing an increase in the effective bandwidth of a cable television distribution plant in a manner compatible with most common cable television systems. By using methods and systems for simultaneously transmitting a standard analog television signal and a digital data signal in a manner that minimizes interference of each with the other, one or more data carriers may be embedded within one or more analog television channels in accordance with various aspects of the present invention. These combined signals can be transmitted over the existing cable television distribution plant to a location at or near the subscribers so that, among other things, that the subscriber may “pause and resume” much in the way Personal Video Recorders work.
Various approaches to upstream signaling for session establishment and channel change within a network are also known in the art. For example, U.S. Pat. No. 6,742,187 to Vogel issued May 25, 2004 and entitled “Upstream bandwidth allocation map (MAP)-initiated channel change method for data-over-cable systems” discloses a method by which an upstream channel change for a cable modem in a data-over-cable system is achieved via an upstream bandwidth allocation map message sent from a cable modem termination system to cable modems, instead of requiring an exchange of upstream channel change request and reply messages. The result is that the upstream channel change can be made essentially immediately, in a deterministic fashion. As such, the upstream channel change method is particularly useful for time-sensitive applications, such as Internet telephony, VoIP, and Internet video on demand services. Load balancing can also be achieved more efficiently.
United States Patent Publication No. 20040163109 to Kang, et al. published Aug. 19, 2004 and entitled “Method for controlling network digital broadcasting service and system therefore” discloses a method of servicing requests associated with the broadcasting of SD (Standard) level and HD (High Definition) level content over a network (e.g., a Digital Subscriber Line). The method comprises providing a direct request (control message) to a digital broadcast server from a client device for a session connection, and establishing a session by receiving a confirmation from the digital broadcasting server. This approach bypasses the SRM (i.e., is direct between the client device and server), thereby ostensibly streamlining the process. Also, a server for a channel change can be requested directly from the client device, the channel change being completed by receiving a confirmation from the server. Other direct client-server requests and confirmations include messages for checking the status of the client device, and for session termination.
While the prior art referenced above (including the SRM function) has generally identified the need for bandwidth management functions and upstream or reverse channel signaling, it fails to provide any apparatus or method that optimizes or conserves bandwidth when both next-generation (e.g., HD) and current generation (e.g., SD) content are present, especially in the instance of SD/SD and SD/HD simulcasts. Furthermore, the prior art SRMs and algorithms are not flexible with regard to allowing selective implementation of one or more business policies with the network, or even within a single local service area or group, and do not leverage efficiencies relating to “switched digital” channel bandwidth allocation for purposes of creating real time HD broadcast sessions.
Hence, based on the foregoing, there is a distinct need for improved apparatus and methods that permit the efficient use and conservation of available bandwidth on content-based networks, such that varying degrees of both present-generation (e.g., SD) and -next generation (e.g., HD) services can be easily and reliably provided to the largest possible customer base. Such improved apparatus and methods would ideally (i) be implemented with only minimal modification to the existing infrastructure, (ii) allow for longer-term migration to different service mixtures (e.g., increased use of HD, VOD, and similar services over time), and (iii) allow for dynamic variation of the mixture of services as a function of one or more parameters such as time of day, service area, service class, etc., including for example leveraging a “switched digital” system architecture for broadcasting HD content. Mechanisms to implement different types of operational and/or business rules would also be provided.